Multiple inheritance, super() and changing signature

[Ben Finney]

Nagy László Zsolt <gandalf at shopzeus.com> writes:

> > [...] 
> >> class BootstrapDesktop(BootstrapWidget, BaseDesktop):
> >>     def __init__(self, appserver, session):
> >>         # there is NOTHING else here, it just connects bootstrap widget
> >> implementation with desktop methods
> >>         super(BootstrapDesktop, self).__init__(appserver, session)
> > The correct way to do that is to simply not define an __init__ method at
> > all.
> But I have to initialize some default attributes.

Then the statement “there is NOTHING else here” must be false. Either
the custom ‘__init__’ does something useful, or it doesn't.

> > See this explanation of C3 linearisation here:
> >
> > https://www.python.org/download/releases/2.3/mro/
> I do not use diamond shapes in my hierarchy, I guess that does not
> affect me. I may be wrong.

With classes all inheriting ultimately from ‘object’ (as all Python 3
classes do, and as all current Python 2 classes should), mutliple
inheritance inevitably places your classes in a diamond inheritance
pattern. And, what's more, you can't know when writing a class whether
it participates in a multiple inheritance hierarchy!

So in practice you must write every class so that it will behave well in
a diamond inheritance pattern.

All this is covered in Raymond Hettinger's material, so it's best that I
just leave you to read that.

-- 
 \        “If the arguments in favor of atheism upset you, explain why |
  `\        they’re wrong. If you can’t do that, that’s your problem.” |
_o__)                                     —Amanda Marcotte, 2015-02-13 |
Ben Finney